Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 3rd Term
Week: 4
Age: 15 years
Duration: 45 minutes
Subject: Physics
Curriculum Theme: Physics
Previous Lesson: Physics in Technology.
Topic: EQUILIBRIUM OF FORCES
Subject Matter: Resultant force, equilibrant force, parallel forces, moment of a force, turning effect, conditions for equilibrium, principle of moments, verification of principle of moment using simple apparatus

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define resultant force and equilibrant force.
Explain the concept of moment of a force and turning effect.
State the principle of moments.
Explain the conditions necessary for an object to be in equilibrium.

Affective Domain:

Appreciate the importance of balanced forces in everyday structures and machines.
Demonstrate careful observation and recording during practical activities.

Psychomotor Domain:

Calculate simple moments of forces.
Set up apparatus to verify the principle of moments.
Apply the principle of moments to solve simple problems.

Collaborate effectively with peers during group practical work.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Senior Secondary Schools.
State Unified Scheme of Work for Physics (SSS 1).
Anyakoha, M. W. (2018). New School Physics for Senior Secondary Schools. Africana First Publishers Plc.

Instructional Materials

The teacher will teach this lesson with the aid of:

Meter rule
Knife edge/fulcrum
Weights
Strings
Clamp stand
Chalkboard
Worksheets with problems

Rationale for the Lesson

This lesson helps pupils understand how forces balance each other, which is important for understanding the stability of objects and structures around them. It enables pupils to apply the principles of forces to real-world situations, from simple levers to building designs.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of forces, their types, and methods of measurement.

Lesson Content/Board Summary

EQUILIBRIUM OF FORCES

Resultant Force

The resultant force is a single force that produces the same effect as two or more forces acting together on an object. It represents the net effect of all forces acting on a body.

Equilibrant Force

The equilibrant force is a single force that, when applied to an object, brings it into equilibrium. It is equal in magnitude and opposite in direction to the resultant force.

Parallel Forces

Parallel forces are forces acting on a body that are parallel to each other. They can be in the same direction (like parallel forces) or in opposite directions (unlike parallel forces).

Moment of a Force (Turning Effect)

The moment of a force about a point (or pivot) is the product of the force and the perpendicular distance from the pivot to the line of action of the force.

Moment = Force × Perpendicular distance

The unit of moment is Newton-metre (Nm). Moments can cause a turning effect, which can be clockwise or anti-clockwise.

Principle of Moments

The principle of moments states that for a body to be in equilibrium, the sum of the clockwise moments about any point must be equal to the sum of the anti-clockwise moments about the same point.

Conditions for Equilibrium

For an object to be in complete equilibrium, two conditions must be met:

The vector sum of all forces acting on the object must be zero (translational equilibrium). This means there is no net force causing linear acceleration.
The vector sum of all moments (torques) about any point must be zero (rotational equilibrium). This means there is no net moment causing angular acceleration.

Verification of Principle of Moments Using Simple Apparatus

The principle of moments can be verified using a meter rule, weights, and a fulcrum. The meter rule is balanced on a knife edge, and known weights are hung at different distances from the fulcrum. By adjusting the weights and distances until the rule is balanced, the clockwise and anti-clockwise moments can be calculated and compared to show they are equal.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils, reviews the previous lesson on types of forces, and introduces the topic “Equilibrium of Forces” by asking pupils what happens when forces are balanced or unbalanced.
Pupils’ Activity: Pupils respond to questions and listen attentively.
Learning Point: Pupils recall previous knowledge and are introduced to the new topic.

Step 2: Resultant and Equilibrant Forces

Time: 8 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines resultant force and equilibrant force, giving simple examples of how they apply in different scenarios.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand the definitions and concepts of resultant and equilibrant forces.

Step 3: Moment of a Force (Turning Effect)

Time: 8 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher defines moment of a force, explains the formula (Moment = Force × Perpendicular distance), its unit, and demonstrates turning effects using a door or a spanner. The teacher also explains clockwise and anti-clockwise moments.
Pupils’ Activity: Pupils observe the demonstration, listen, and calculate simple moments as guided by the teacher.
Learning Point: Pupils understand how forces can cause turning effects and how to calculate moments.

Step 4: Principle of Moments and Conditions for Equilibrium

Time: 8 minutes
Teaching Skill: Explanation/Statement
Teacher’s Activity: The teacher states the principle of moments clearly and explains the two conditions for an object to be in complete equilibrium (zero net force and zero net moment).
Pupils’ Activity: Pupils listen, write down the principle and conditions, and ask questions.
Learning Point: Pupils learn the principle of moments and the conditions required for equilibrium.

Step 5: Practical Verification of Principle of Moments

Time: 10 minutes
Teaching Skill: Demonstration/Guidance
Teacher’s Activity: The teacher guides pupils to set up the apparatus (meter rule, weights, fulcrum) to practically verify the principle of moments. The teacher demonstrates how to balance the meter rule and calculate moments.
Pupils’ Activity: Pupils work in groups to set up the apparatus, take readings, calculate clockwise and anti-clockwise moments, and observe the balance.
Learning Point: Pupils gain practical experience and verify the principle of moments.

Step 6: Application of Principle of Moments

Time: 4 minutes
Teaching Skill: Problem Solving
Teacher’s Activity: The teacher presents a few simple problems involving the principle of moments and guides pupils through the solutions.
Pupils’ Activity: Pupils attempt to solve the problems and participate in discussions of the solutions.
Learning Point: Pupils apply the principle of moments to solve numerical problems.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define resultant force and equilibrant force.
What is the moment of a force? State its unit.
State the principle of moments.
Mention two conditions for an object to be in equilibrium.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson and gives homework, which includes solving more problems related to the principle of moments.
Pupils’ Activity: Pupils listen to the summary and copy the homework.
Learning Point: Pupils consolidate their understanding of the lesson.

Lesson Keywords

Resultant force – A single force that produces the same effect as multiple forces acting on an object.
Equilibrant force – A force that balances other forces, equal in magnitude and opposite in direction to the resultant force.
Parallel forces – Forces that act parallel to each other.
Moment of a force – The turning effect of a force about a pivot, calculated as force multiplied by perpendicular distance.
Turning effect – The tendency of a force to cause rotation about an axis or pivot.
Equilibrium – A state where an object has no net force and no net moment acting on it, resulting in no change in its state of motion.
Principle of moments – For a body in equilibrium, the sum of clockwise moments equals the sum of anti-clockwise moments about any point.

Differentiation

For pupils who are struggling, the teacher will provide additional one-on-one support during the practical session and offer simpler problems. For advanced pupils, more complex problems involving multiple forces and varying angles can be provided as an extension activity.

Note for teachers using this lesson plan

Ensure all instructional materials are prepared and checked before the lesson. Emphasize safety during the practical verification. Encourage active participation and group collaboration among pupils. Use clear diagrams on the board to illustrate concepts like moments and forces.